Method and device for driving a motor vehicle with hybrid drive

ABSTRACT

A method for driving a motor vehicle includes selecting a drive mode. The motor vehicle has a hybrid drive including an internal combustion engine and an electric machine for providing a drive torque (t) for driving the motor vehicle. The motor vehicle is drivable by a torque of the internal combustion engine, by virtue of the internal combustion engine being started, or by a torque of the electric machine. The method includes detecting an amount of running activity (t B ) of the internal combustion engine. The drive mode is selected based on the detected amount of running activity (t B ).

CROSS REFERENCE TO RELATED APPLICATIONS

Priority is claimed to German Patent Application No. DE 10 2013 107330.1, filed on Jul. 11, 2013, the entire disclosure of which is herebyincorporated by reference herein.

FIELD

The present invention relates to a method for driving a motor vehiclehaving a hybrid drive, a hybrid drive of a motor vehicle, and a motorvehicle drive train including a hybrid drive comprising an internalcombustion engine and an electric machine.

BACKGROUND

In the field of hybrid drive systems, it is generally known for themotor vehicle to be driven purely electrically by means of the electricmachine or driven exclusively by means of the internal combustionengine. It is also known, upon start-up of the motor vehicle, that is tosay in the event of a key-initiated start, for the internal combustionengine to be started by means of the electric machine and for the motorvehicle to be driven by means of the internal combustion engine, or,upon start-up of the motor vehicle, for only the electric machine to beused to drive the motor vehicle and, if appropriate, for the internalcombustion engine to be started during travel by being drag-started bymeans of the electric machine.

A disadvantage of the internal combustion engine being started bydrag-starting during travel is that, during said process, the tractionbattery of the motor vehicle is subject to intense load and undercertain conditions the traction battery can sustain permanent damage.Furthermore, the internal combustion engine is generally subject tohigher wear when started by drag-starting by means of the electricmachine than when started by cranking by means of the electric machine,such that under certain conditions, such a start by drag-starting shouldbe avoided.

DE 10 2012 000 036 A1 discloses a method for the start-up of an internalcombustion engine of a hybrid drive, in which method a torque for thestart-up of the internal combustion engine is set as a function of atemperature of the internal combustion engine. A disadvantage here isthat consideration is not given to all influential variables andstart-up variations that have a significant influence on wear of theinternal combustion engine.

DE 102 46 978 A1 discloses a method for the starting of a drive unit ofa motor vehicle, in which method different modes for the starting of theinternal combustion engine are set as a function of a temperature of theinternal combustion engine. A disadvantage here is that consideration isnot given to the wear in the event of drag-starting by means of theelectric motor.

SUMMARY

In an embodiment, the present invention provides a method for driving amotor vehicle having a hybrid drive including an internal combustionengine and an electric machine for providing a drive torque (t) fordriving the motor vehicle. The motor vehicle is drivable by a torque ofthe internal combustion engine, by virtue of the internal combustionengine being started, or by a torque of the electric machine. The methodincludes detecting an amount of running activity (t_(B)) of the internalcombustion engine. A drive mode is selected based on the detected amountof running activity (t_(B)).

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in even greater detail belowbased on the exemplary figures. The invention is not limited to theexemplary embodiments. All features described and/or illustrated hereincan be used alone or combined in different combinations in embodimentsof the invention. The features and advantages of various embodiments ofthe present invention will become apparent by reading the followingdetailed description with reference to the attached drawings whichillustrate the following:

FIG. 1 schematically shows a motor vehicle having a hybrid drivetrainand a control unit for the control of the drive assemblies of the hybriddrivetrain; and

FIG. 2 shows a diagram for explaining the running-activity-dependenttemperature threshold value.

DETAILED DESCRIPTION

An aspect of the present invention provides a reduction of the wear ofan internal combustion engine of a hybrid drivetrain in particular in arunning-in phase of the internal combustion engine.

In an embodiment, the present invention provides a method for driving amotor vehicle having a hybrid drive, wherein the hybrid drive has aninternal combustion engine and an electric machine for providing a drivetorque for driving the motor vehicle, wherein the motor vehicle can bedriven either by means of a torque of the internal combustion engine, byvirtue of the internal combustion engine being started, or by means of atorque of the electric machine, by virtue of the electric machine beingactivated.

In another embodiment the present invention provides a device forcontrolling a hybrid drive of a motor vehicle, wherein the hybrid drivehas an internal combustion engine and an electric machine for providinga drive torque for driving the motor vehicle, wherein the motor vehiclecan be driven by means of a torque of the internal combustion engine orby means of a torque of the electric machine.

In another embodiment the present invention provides a motor vehicledrivetrain having a hybrid drive which has an internal combustion engineand an electric machine.

In an embodiment, the present invention provides a method in which anamount of running activity of the internal combustion engine is detectedand the drive mode is selected on the basis of the detected amount ofrunning activity.

Furthermore, in an embodiment, the present invention provides a deviceincluding a running activity detection unit, which is designed to detectthe amount of running activity of the internal combustion engine, and acontrol unit which is designed to either activate the internalcombustion engine so as to drive the motor vehicle, or activate theelectric machine so as to drive the motor vehicle, on the basis of thedetected amount of running activity.

Further, in an embodiment, the present invention provides a motorvehicle drivetrain including a device for controlling the hybriddrivetrain, as described above.

By virtue of the fact that the drive mode is selected on the basis ofthe detected amount of running activity, it is possible in the case oflow amounts of running activity, when the internal combustion engine hasnot yet been run in, to dispense with the electric drive upon driveawayand the associated starting method of drag-starting by means of theelectric machine, such that, during the sensitive running-in phase, theinternal combustion engine can be protected against excessive wear.Since the driving of the motor vehicle by means of the internalcombustion engine in the case of low amounts of running activity is moregentle and generally avoids a wear-intensive start of the internalcombustion engine by drag-starting, it is thus possible for unnecessarywear to be avoided in the running-in phase of the internal combustionengine and for the service life of the internal combustion engine to beincreased overall.

The object of the present invention is thus achieved in its entirety.

In a preferred embodiment, the temperature of the internal combustionengine is determined and the drive mode is furthermore selected on thebasis of the detected temperature of the internal combustion engine.

In this way, consideration can be given to a further wear-influencingfactor, and the advantages of the hybrid drive at the correspondingtemperature of the internal combustion engine can be utilized.

In a further preferred embodiment, the motor vehicle is driven by meansof the internal combustion engine if the temperature is lower than apredefined temperature threshold value.

In this way, starting of the internal combustion engine by drag-startingby means of the electric machine can be avoided at low temperatures.

It is furthermore preferable for the motor vehicle to be driven by meansof the electric machine if the temperature is higher than the predefinedtemperature threshold value.

In this way, the advantages of the hybrid drive can be utilized withlittle wear if the temperature of the internal combustion engine isabove a critical temperature.

It is also preferable for the predefined temperature threshold value tobe reduced as a function of the detected amount of running activity.

In this way, a relatively high temperature threshold value can bedefined in the case of low amounts of running activity, and a lowertemperature threshold value can be defined with progressive runningactivity, such that, with progressive running activity, the hybrid drivecan be fully utilized and, at the same time the internal combustionengine is preserved in the case of low amounts of running activity.

It is furthermore preferable if the predefined temperature is, after apredefined amount of running activity, reduced from a first temperaturevalue to a second temperature value.

In this way, after running-in the internal combustion engine, thetemperature threshold value can be reduced to such an extent that thehybrid drive can be fully utilized.

It is furthermore preferable for the predefined amount of runningactivity to correspond to a running-in phase of the internal combustionengine.

In this way, the internal combustion engine can be preserved in therunning-in phase and fully utilized after the running-in phase.

It is furthermore preferable for the amount of running activity tocorrespond to a distance travelled by the motor vehicle.

In this way, the amount of running activity can be determined withlittle technical outlay.

It is furthermore preferable for the amount of running activity to be anoperating duration of the internal combustion engine.

In this way, the amount of running activity of the internal combustionengine can be precisely determined.

It is furthermore preferable for the drive mode to be selected upon thestart-up of the motor vehicle, and for the motor vehicle to be drivencorrespondingly for driveway purposes.

In this way, upon driveaway of the motor vehicle, the need for startingby drag-starting is eliminated.

Overall, by means of the present invention, the wear of the internalcombustion engine preferably in a running-in phase can be reduced, andthus the performance of the drive as a whole and the service life of theinternal combustion engine can be increased. By virtue of thetemperature of the internal combustion engine being taken intoconsideration, it is possible for particularly wear-intensivesituations, such as for example the drag-starting of the internalcombustion engine at a very low temperature, to be avoided, whereby theinternal combustion engine as a whole and the traction battery can beconserved.

In FIG. 1, a motor vehicle is schematically illustrated and is denotedgenerally by the reference numeral 10. The motor vehicle 10 has adrivetrain 12 which, in the present case, comprises an electric machine14 and an internal combustion engine 16 for providing drive power. Thedrivetrain serves for driving driven wheels 18R, 18L of the motorvehicle 10. The internal combustion engine 16 is connected orconnectable to the electric machine 14 via a crankshaft 20, wherein theinternal combustion engine 16 and the electric machine 14 provide adrive torque t at a drive output shaft 22. The drive output shaft 22 isconnected or connectable to the driven wheels 18R, 18L via atransmission unit 24 and a differential gear 26 in order to transmit thedrive torque t to the driven wheels 18R, 18L. The crankshaft 20 and thedrive output shaft 22 each have a clutch 28, 30 for detachablyconnecting the internal combustion engine 16 to the electric machine 14,and the electric machine 14 to the transmission unit 24, respectively.

The internal combustion engine 16 is connectable to the electric machine14 by means of the clutch 28 in order to transmit a torque of theinternal combustion engine 16 to the electric machine 14. The rotor ofthe electric machine 14 is connected to the drive output shaft 22 inorder to transmit the drive torque t via the transmission unit 24 andthe differential to the driven wheels 18R, 18L. The torque t may,depending on the operating mode, be formed by the torque of the electricmachine 14, the torque of the internal combustion engine 16 or by a sumof the two torques.

The electric machine 14 is activated, and supplied with electricalenergy, by means of an inverter 32. The inverter is connected to anenergy supply unit 34 or an electrical energy store 34 (for examplebattery) of the vehicle 10 and serves for converting a direct-currentvoltage provided by the energy supply unit 34 into alternating currentin general or into a number of phase currents of the phases of theelectric machine 14.

The motor vehicle 10 has a control unit 36 which is connected to theinternal combustion engine 16 and to the inverter 32 and control thesecorrespondingly. The internal combustion engine 16 is assigned atemperature sensor 38 which detects a temperature of the internalcombustion engine 16, preferably an oil temperature of the internalcombustion engine 16, and transmits the detected data to the controlunit 36.

For the starting and driveaway of the motor vehicle 10, it is possibleon the one hand for only the electric machine 14 to be used and to beactivated correspondingly by the control unit 36 via the inverter 32,wherein the clutch 28 is opened, such that the motor vehicle 10 isdriven purely electrically. Alternatively, the internal combustionengine 16 may be started and the motor vehicle 10, with clutches 28 and30 closed, the drive torque t corresponds to the torque of the internalcombustion engine 16 and optionally additionally the torque of theelectric machine 14, such that the motor vehicle 10 is driven undermotor power.

Accordingly, when the motor vehicle 10 is at a standstill, for exampleupon start-up of the vehicle 10, the so-called key-initiated start, theinternal combustion engine 16 may be started by means of the electricmachine 14 via the crankshaft 20 or by means of a separate starter 40.If, during the start-up of the motor vehicle 10, only the electricmachine 14 is used for the driveaway of the motor vehicle 10, theinternal combustion engine 16 may be drag-started during travel byclosing the clutch 28. The drag-starting of the internal combustionengine 16 by means of the electric machine 14 subjects the battery 34 tointense loading, such that drag-starting can be permitted only undercertain conditions. Furthermore, the wear of the internal combustionengine 16 is increased under certain conditions, for example at very lowtemperatures, such that said drag-starting should be avoided.

Purely electric driveaway by means of the electric machine 14 and theassociated drag-starting of the internal combustion engine 16 ispermitted as a function of the temperature of the internal combustionengine 16 and as a function of an amount of running activity of theinternal combustion engine 16. For this purpose, the control unit 36 isassigned a running activity detection unit 42 which detects the amountof running activity of the internal combustion engine 16. Here, theamount of running activity may be detected either as an operatingduration of the internal combustion engine 16 or, in general, as anumber of kilometers travelled by the motor vehicle 10. If thetemperature sensor 38 detects a temperature value of the internalcombustion engine 16 which lies below a threshold temperature, and therunning activity of the internal combustion engine 16 has not yetreached a certain value, only a driveaway of the motor vehicle 10 bymeans of the internal combustion engine 16 is permitted. The detectionof the temperature and of the amount of running activity is performedpreferably upon the starting of the motor vehicle and the correspondingoperating mode is selected, though this may also be performed during astoppage in travel, for example in the context of a start-stop function.If, upon starting, the temperature of the internal combustion engine 16falls below the predefined value for the detected amount of runningactivity, the key-initiated start corresponds to a start of the internalcombustion engine 16. If the temperature of the internal combustionengine 16 falls below the predefined value, drag-starting during travelcan be permitted, such that in this case, the key-initiated startcorresponds to the starting of the electric machine 14.

In this way, by means of the detection of the temperature of theinternal combustion engine and of the amount of running activity of theinternal combustion engine, the drive mode can be selected by means ofthe control unit, and the internal combustion engine 16 can beactivated, or the electric machine 14 can be activated via the inverter32, by the control unit 36. The predefined temperature threshold valuemay preferably be set to be constant during a running-in phase of theinternal combustion engine 16 and reduced to a second value after thecompletion of the running-in phase and kept constant for the remainderof the running of the motor vehicle. Alternatively, the temperaturethreshold value may also be reduced in continuous fashion, orcorresponding to a predefined function, as a function of the amount ofrunning activity of the internal combustion engine 16, andcorrespondingly approach a target value asymptotically.

By means of the selection of the drive mode as a function of thetemperature of the internal combustion engine 16 and as a function ofthe amount of running activity of the internal combustion engine 16, thewear of the components and in particular of the internal combustionengine 16 and of the battery 34 can be reduced.

FIG. 2 schematically illustrates a profile T_(s) of the temperaturethreshold value as a function of the amount of running activity t_(B) ofthe internal combustion engine 16.

The temperature threshold value T_(s) is illustrated by dashed lines andis set to be constant up to an amount of running activity t_(B) of theinternal combustion engine 16 of 15 operating hours. Said firsttemperature threshold value T₁ is in this case 15° C. After the amountof running activity of 15 operating hours has elapsed, the temperaturethreshold value T_(s) is reduced to a second temperature threshold valueT₂. Above the, in this case, dashed line of the temperature thresholdvalue T_(s), a key-initiated start corresponds to an electric start ofthe electric machine 14, and below the dashed line of the temperaturethreshold value T_(s), a key-initiated start is a start of the internalcombustion engine 16. The time until the first 15 operating hours haselapsed, which corresponds to a distance travelled of approximately 1000kilometers, forms the running-in phase of the internal combustion engine16. After the running-in phase, below 0° C., the starting of theinternal combustion engine 16 is performed as the initial start when themotor vehicle 10 is started up.

It is self-evident that, for different engine types, the running-inphase can be defined to be longer or shorter, and the first temperaturethreshold value T₁ and the second temperature threshold value T₂ may beset to other values.

A continuous reduction of the temperature threshold value T_(s), or areduction in multiple stages, is also conceivable.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive. Itwill be understood that changes and modifications may be made by thoseof ordinary skill within the scope of the following claims. Inparticular, the present invention covers further embodiments with anycombination of features from different embodiments described above andbelow.

The terms used in the claims should be construed to have the broadestreasonable interpretation consistent with the foregoing description. Forexample, the use of the article “a” or “the” in introducing an elementshould not be interpreted as being exclusive of a plurality of elements.Likewise, the recitation of “or” should be interpreted as beinginclusive, such that the recitation of “A or B” is not exclusive of “Aand B,” unless it is clear from the context or the foregoing descriptionthat only one of A and B is intended. Further, the recitation of “atleast one of A, B and C” should be interpreted as one or more of a groupof elements consisting of A, B and C, and should not be interpreted asrequiring at least one of each of the listed elements A, B and C,regardless of whether A, B and C are related as categories or otherwise.Moreover, the recitation of “A, B and/or C” or “at least one of A, B orC” should be interpreted as including any singular entity from thelisted elements, e.g., A, any subset from the listed elements, e.g., Aand B, or the entire list of elements A, B and C.

What is claimed is:
 1. A method for driving a motor vehicle having ahybrid drive that includes an internal combustion engine and an electricmachine for providing a drive torque (t) for driving the motor vehicle,the motor vehicle being drivable by a torque of the internal combustionengine, by virtue of the internal combustion engine being started, or bya torque of the electric machine, the method comprising: detecting anamount of running activity (t_(B)) of the internal combustion engineusing a running activity detection unit, the amount of running activity(t_(B)) being one of a total distance travelled by the motor vehicle ora total operating duration of the internal combustion engine;determining a temperature of the internal combustion engine using atemperature sensor; selecting, using a control unit, a drive mode basedon the detected amount of running activity (t_(B)) and the determinedtemperature of the internal combustion engine; and driving the motorvehicle by at least one of the internal combustion engine or theelectric machine based on the selected drive mode.
 2. The method asrecited in claim 1, wherein the motor vehicle is driven by the internalcombustion engine if the determined temperature is lower than apredefined temperature threshold value (Ts).
 3. The method as recited inclaim 2, wherein the predefined temperature threshold value (Ts) isreduced as a function of the detected amount of running activity(t_(B)).
 4. The method as recited in claim 3, wherein the predefinedtemperature threshold value (Ts) is, after a predefined amount ofrunning activity, reduced from a first threshold value (T₁) to a secondthreshold value (T₂).
 5. The method as recited in claim 4, wherein thepredefined amount of running activity (t_(B)) corresponds to arunning-in phase of the internal combustion engine.
 6. The method asrecited in claim 1, wherein the motor vehicle is driven by the electricmachine if the determined temperature is higher than the predefinedtemperature threshold value (Ts).
 7. The method as recited in claim 6,wherein the predefined temperature threshold value (Ts) is reduced as afunction of the detected amount of running activity (t_(B)).
 8. Themethod as recited in claim 7, wherein the predefined temperaturethreshold value (Ts) is, after a predefined amount of running activity,reduced from a first threshold value (T₁) to a second threshold value(T₂).
 9. The method as recited in claim 8, wherein the predefined amountof running activity (t_(B)) corresponds to a running-in phase of theinternal combustion engine.
 10. The method as recited in claim 1,wherein the drive mode is selected upon the start-up of the motorvehicle, and the motor vehicle is driven correspondingly for driveawaypurposes.
 11. A device for controlling a hybrid drive of a motorvehicle, the hybrid drive having an internal combustion engine and anelectric machine for providing a drive torque (t) for driving the motorvehicle, the motor vehicle being drivable by a torque of the internalcombustion engine or by a torque of the electric machine, the devicecomprising: a running activity detection unit configured to detect anamount of running activity (t_(B)) of the internal combustion engine,the amount of running activity (t_(B)) being one of a total distancetravelled by the motor vehicle or a total operating duration of theinternal combustion engine; a temperature sensor configured to determinea temperature of the internal combustion engine; and a control unitconfigured to selectively activate either the internal combustion engineso as to drive the motor vehicle or the electric machine so as to drivethe motor vehicle, based on the detected amount of running activity(t_(B)) and the determined temperature.
 12. A motor vehicle drivetrainfor driving a motor vehicle, the drive train comprising: a hybrid driveincluding an internal combustion engine and an electric machine fordriving the motor vehicle, the motor vehicle being drivable by a torqueof the internal combustion engine or by a torque of the electricmachine; and a device for controlling the hybrid drive including: arunning activity detection unit configured to detect an amount ofrunning activity (t_(B)) of the internal combustion engine, the amountof running activity (t_(B)) being one of a total distance travelled bythe motor vehicle or a total operating duration of the internalcombustion engine; a temperature sensor configured to determine atemperature of the internal combustion engine; and a control unitconfigured to selectively activate either the internal combustion engineso as to drive the motor vehicle or the electric machine so as to drivethe motor vehicle, based on the detected amount of running activity(t_(B)) and the determined temperature.